Hydrodimerization of acrylic acid derivatives



United States Patent U.S. Cl. 260-4653 11 Claims ABSTRACT OF THE DISCLOSURE Functional derivatives of acrylic acid are hydrodimerized to the corresponding adipic acid derivatives using alkali metal amalgam within a reaction medium comprising either aqueous or anhydrous ammonia, the latter containing a dissolved ammonium or amine salt.

The present invention concerns the hydrodimerization of functional derivatives of acrylic acid selected from the group consisting of acrylonitrile, lower-alkyl acrylonitrile and lower alkyl acrylates, to form corresponding adipic acid derivatives. The adipic acid derivatives prepared in accordance with the present invention are useful as reactants in the manufacture of polyamide fibres and polyamide plastics in general.

The hydrodimerization of acrylic acid derivatives is known. The processes used, or proposed for use, up to now are classifiable in two groups: (a) electrolytic hydrogenation, (b) reduction by alkali metal amalgam or, in some cases, alkaline earth metal amalgam. The present invention concerns a process of the second group.

Known processes for the hydrodimerization of acrylic acid derivatives using an alkali metal amalgam all proceed in aqueous media comprising as solute any of the oompounds dimethyl sulfoxide, sulfonal, formamide, methyl formamide, dimethyl formamide, methyl acetamide, dimethyl acetamide and various quaternary ammonium salts. The drawback of all these known processes is that for the preparation of the aqueous media relatively high proportions of relatively expensive solutes are required. Even if these solutes are recuperated at the end of the reaction such recuperation invariably involves certain losses. In addition, recuperation often inecessitates repeated distillation of rather high boiling liquids resulting in slight decomposition of the latter with the consequential formation of undesirable contaminants.

The present invention is based on the surprising observation that acrylic acid derivatives may be hydrodimerized with the use of an alkali metal amalgam within a reaction medium comprising ammonia.

Consequently, the invention consists in a process for the hydrodimerization of acrylic acid derivatives, selected from the group consisting of acrylonitrile, lower alkyl acrylonitrile and lower alkyl acrylates, using an alkali metal amalgam as reducing agent, wherein the reaction medium comprises ammonia.

According to one embodiment, the ammoniacal reaction medium is aqueous, provided the relative proportions of Water and ammonia on one hand and that of the acrylic acid derivative on the other hand, are kept within certain limits.

This embodiment thus consists in a process for the hydrodimerization of an acrylic acid derivative using an alkali metal amalgam as reducing agent, wherein the reaction medium is aqueous ammonia in which the ammonia: water ratio is within the range of from 15 :l to 0.3 1, preferably of from 3:1 to 1:1, and the amount of the acrylic 3,519,674 Patented July 7, 1970 ice acid derivative in the reaction mixture is within the range of from 2 to 30% by weight, preferably from 5 to 10% by weight.

The temperature at which the process may be carried out may range from 40 C. to +30 C. where the reaction is carried out within the range of from -40 C. to -10 C. it is a rule possible to work with open vessels under atmospheric pressure. Against this, at higher temperatures, it is necessary to work in closed vessels.

According to another embodiment of the invention, the ammoniacal reaction medium is anhydrous consisting of liquid ammonia in which an ammonium or amine salt is dissolved.

While practically all ammonium and amine salts can be used for this embodiment, the cheap inorganic salts, especially ammonium chloride and ammonium sulfate, are preferred in the performance of the process of the present embodiment on a technical scale. Also, it has been found that the use, of, for example, ammonium chloride makes for a smaller by-production of propionic acid derivatives than the use of, for example, triethylamine hydrocholoride.

The use of liquid ammonia provides great advantages from the engineering point of view, since after the termination of the reaction the liquid ammonia can simply be allowed to evaporate, leaving as a residue merely the reaction products and any unconverted starting material in admixture with a solid salt sediment from which the reaction products can readily be separated mechanically. Of course, the reaction itself will have to be carried out at so low a temperature that no appreciable evaporation of the ammonia takes place during the reaction itself. Since the boiling point of ammonia under atmospheric pressure is 33 C., a reaction temperature in the neighborhood of 30 C. is a preferred one. The evaporated ammonia can, of course, be recovered.

This embodiment, therefore, requires simpler and more compact apparatus than does the process according to the first embodiment.

It is known that together with the hydrodimerization of acrylic acid derivatives there usually occurs a concurring hydrogenation of the monomer. It has been observed that when proceeding in accordance with the present invention this concurring reaction occurs only to a relatively small extent and the amount of the hydr genated monomer does as a rule not exceed 25% calculated on the acrylic acid derivative fed into the reaction, and is in most cases lower.

The process according to the invention has the great advantage that it uses a cheap reaction medium while at the same time producing very satisfactory yields.

A further advantage of the process according to the present invention is that no pH control is required and no neutralizing agent need to be added since the reaction medium is alkaline from the outset and any additional amount of free alkali formed in the course of the reaction is insignificant.

From the various alkali metal amalgams that can be used for the process according to the invention the sodium and potassium amalgams are preferred on account of their ready availability. The concentration of the alkali metal in the amalgam is not critical and may vary within wide limits. The preferred range is within the limit of 0.01 to 0.5% by weight.

The invention is illustrated by the following examples Without being limited thereto.

EXAMPLE 1 A solution of 10 g. of acrylonitrile and g. of ammonia in 30 g. of water was cooled to 30 C. in a Dry Ice-isopropanol bath. In another flask 2 kg. of sodium amalgam (0.3% by weight of sodium content) were cooled to the same temperature. The solution was poured onto the amalgam and the reaction mixture was maintained at 30 C. under slow swirling for 5 minutes. The amalgam was then separated, ammonia was distilled off, the solution diluted with water and extracted with methylene chloride. The methylene chloride extract contained the reaction product. Gas chromatographic analysis showed that it consisted of 85% of adiponitrile and 5% of propionitrile calculated on the acrylonitrile feed.

The combined metal conversion yield for adiponitrile and propionitrile was 92%.

From the methylene chloride solution adiponitrile and propionitrile were separately recovered by fractional distillation. Methylene chloride and propionitrile distilled under atmospheric pressure. The adiponitrile was then distilled at a reduced pressure BP 182 C./20 mm. Hg.

EXAMPLE 2 A solution of 10 g. of acrylonitrile and 100 g. of ammonia in 50 g. of water was treated with sodium amalgam at 20 C. as described in Example 1. The products obtained consisted of 72% of adiponitrile and 11% of propionitrile calculated on the acrylonitrile feed, determined as described in Example 1.

The metal conversion yield was 89.

The recovery of the product from the methylene chloride solution was as in Example 1.

EXAMPLE 3 2.5 kg. of sodium amalgam containing 0.3% by weight of sodium was introduced into a thick walled flask and 10 g. of acrylonitrile and 50 g. of Water into another flask communicating with the former. The second flask was connected to a vacuum system and also through a control valve to a source of ammonia. The flask with the acrylonitrile and water was cooled in liquid air and evacuated. Thereafter the control valve leading to the ammonia source was opened and 50 gr. of ammonia were distilled into the cold flask. Thereafter the flask was sealed off from the vacuum system and also from the ammonia source. The two communicating flasks were introduced into an ice bath and when the temperature reached C. in both flasks the contents of the two flasks were mixed and the reaction allowed to proceed for minutes under gentle swirling. The reaction mixture was worked up and the composition was determined as described in Example 1. The product consisted of 50% of adiponitrile and 21% of propionitrile calculated on the acrylonitrile feed.

EXAMPLE 4 A solution of g. of l-methyl acrylonitrile and 90 g. of ammonia in 30 g. of water was reacted for minutes with 2 kg. of amalgam containing 0.3% by weight of sodium. A sample of reaction solution, separated from amalgam, was extracted with methylene chloride and analysed by gas chromatography which showed that the product contained 70% of dimethyl adiponitrile and 10% of isobutyronitrile calculated on the l-methyl acrylonitrile feed.

From the aqueous reaction mixture separated from the amalgam the ammonia was distilled oil and the products were extracted by means of methylene chloride. From the resulting extract the products were recovered by fractional distillation. B.P. dimethyladiponitrile==110 C./ 1 mm. Hg.

EXAMPLE 5 A solution of 10 g. of acrylonitrile and 100 g. of ammonia in 30 g. of water was reacted with 2.5 kg. of potassium amalgam containing 0.5% by weight of potassium. Procedure in the working up was analogous to that described in Example 1. The product consisted of 83% of adiponitrile and 5% of propionitrile calculated on the acrylonitrile feed.

The metal conversion yield was 87%.

4 EXAMPLE 6 A three-neck reaction flask of 500 ml. capacity provided with a Teflonsealed stirrer, a cold finger and a dropping funnel equipped with a cooling jacket was maintained in a cooling bath at 30 C.

A solution of 10 g. of acrylonitrile and 11 g. of NH Cl in 200 cc. of liquid ammonia was introduced into the flask. 2 kg. of sodium amalgam (containing 0.3% by weight of sodium) was cooled to 30 C. in the funnel and then dropped slowly into the reaction flask under constant stirring, while the temperature of the reaction mixture was maintained at 30 C. The spent amalgam was then separated from the reaction mixture and the latter was subjected to fractional distillation at atmospheric pressure. There distilled first the ammonia and then the propionitrile.

Finally, adiponitrile was distilled at reduced pressure (182 C./20 mm. Hg).

The products thus obtained consisted of 9 g. of adiponitrile and 0.5 g. of propionitrile and the yields amounted to adiponitrile and 5% propionitrile based on the weight of the acrylonitrile feed. The metal conversion yield of the combined adiponitrile and propionitrile was 90%.

EXAMPLE 7 A solution of 10 g. of acrylonitrile and 30 g. of triethylamine hydrochloride in 200 cc. of liquid ammonia was treated with sodium amalgam in the manner described in Example 6. The products, were separated similarly as described in Example 6. The yields amounted to 85% adiponitrile and 9% propionitrile, calculated on the weight of the acrylonitrile feed. The metal conversion yield was EXAMPLE 8 A mixture of 10 g. of ethyl acrylate, 6 g. of ammonium chloride and 200 cc. of liquid ammonia was reacted with sodium amalgam in the manner described in Example 6. The products were separated similarly as in Example 6. The yields ammounted to 72% of diethyl adipate and 6% of ethyl propionate, calculated on the weight of the ethyl acrylate feed. The metal conversion yield was 94%.

We claim:

1. In a process for the hydrodimerization of acrylic acid derivatives selected from the group consisting of acrylonitrile, lower alkyl acrylonitrile and lower alkyl acrylates to the corresponding adipic acid derivatives, using an alkali metal amalgam as reducing agent, the improvement which comprises that the reaction medium is aqueous ammonia in which the ammonia:water ratio is within the range of from 15:1 to 03:1 and the amount of acrylic acid derivative in said reaction medium is within the range of from 2 to 30% by weight, said reaction medium being maintained at a temperature of from 40 C. to +30 C.

2. A process as claimed in claim 1, wherein the ammonia:water ratio in the reaction medium is within the range of from 3:1 to 1:1.

3. A process as claimed in claim 1, wherein the amount of acrylic acid derivative in thereaction medium is within the range of from 5 to 10% by weight.

4. A process as claimed in claim 1, wherein the reaction medium is maintained at a temperature of from 40 C. to 10 C.

5. A process as claimed in claim 1, wherein the acrylic acid derivative used as starting material is acrylonitrile and the final adipic acid derivative is adiponitrile.

6. A process as claimed in claim 1, wherein the acrylic acid derivative used as starting material is methacrylonitrile and the final adipic acid derivative is dimethyl-adiponitrile.

7. In a process for the hydrodimerization of acrylic acid derivatives selected from the group consisting of acrylonitrile, lower alkyl-acrylonitrile and lower alkyl acrylates to the corresponding adipic acid derivatives, using an alkali metal amalgam as reducing agent, the improvement which comprises that the reaction medium is anhydrous liquid ammonia in which an ammonium or triethylamine salt of an inorganic acid is dissolved and the amount of acrylic acid derivative in said reaction medium is within the range of from about 2 to 30% by weight, said reaction medium being maintained at a temperature at which no substantial evaporation of liquid ammonia takes place.

8. A process as claimed in claim 7, wherein the ammonium salt is ammonium chloride.

9. A process as claimed in claim 7, wherein the ammonium salt is ammonium sulfate.

10. A process as claimed in claim 7, wherein the triethylamine salt is triethylamine hydrochloride.

11. A process as claimed in claim 7, wherein the reaction medium is maintained at a temperature of about 30 C.

References Cited UNITED STATES PATENTS 3,193,574 7/1965 Katchalsky et al. 260-4658 3,356,708 12/1967 Davies et al. 260465.8

JOSEPH PAUL BRUST, Primary Examiner -U.S. Cl. X.R. 

